When initially launching the application, RoboForm will prompt you to enter your Master Password. This will occur upon the initial launch even if the unlock mode is set to PIN or Touch ID. Moving forward, whenever RoboForm is awake and running in the background, you can unlock the application using your PIN or Touch ID.
For security purposes, the longest period of time the RoboForm "Auto-Logout after" period can be set to is one month. This means that at the very least, you will be required to enter your Master Password to log back into the app after a one month period. The Auto-Logout After setting can be accessed under Settings >> Security >> Auto-Logout after.